Method for removal of hydrogen sulfide

Abstract

A two stage process for removing and subsequently recovering sulfur values from hydrogen sulfide or mercaptan-contaminated feed gas streams is disclosed. The process employs a polyvalent metal ion chelate redox couple to convert S -- to S and uses the metal ion reoxidation gas stream to remove the solid sulfur overhead as a flotation froth. The feed gas stream is contacted with the chelate in a first contacting zone, and additionally in the reoxidation zone.

What is claimed is: 
     
       1. A continuous process for recovering sulfur values from a hydrogen sulfide-containing gaseous stream which comprises the steps of (a) contacting said hydrogen sulfide-containing gaseous stream with an aqueous solution of a water-soluble oxidized polyvalent metal chelate catalyst at alkaline pH thereby converting the hydrogen sulfide to particulate elemental sulfur and reducing the polyvalent metal chelate catalyst and forming a suspension of particulate elemental sulfur in said aqueous solution and a first product gas stream depleted in hydrogen sulfide,   (b) contacting said suspension with free oxygen-containing gas in an oxidation zone under flotation conditions thereby oxidizing the polyvalent metal chelate to its oxidized form and forming a regenerated aqueous solution and introducing into the same oxidation zone into contact with the regenerated aqueous solution said first product gas stream thereby converting remaining hydrogen sulfide in said first product gas stream to elemental sulfur and forming a second product gas stream doubly depleted in hydrogen sulfide and an aqueous liquid phase containing the oxidized polyvalent metal chelate catalyst and a sulfur particle-gas-liquid foam phase,   (c) separating the foam phase from the aqueous liquid phase,   (d) recycling at least a portion of the aqueous liquid phase to the contacting step of (a), and   (e) recovering elemental sulfur from the foam phase.   
     
     
       2. The process of claim 1 wherein the polyvalent metal is iron. 
     
     
       3. The process of claim 1 wherein in step (b) said flotation conditions include sparging free oxygen-containing gas upwards through said suspension. 
     
     
       4. The process of claim 3 wherein in step (c) said separating includes air flotation. 
     
     
       5. The process of claim 1 wherein said gaseous stream contains from about 5 to about 40% by volume of hydrogen sulfide. 
     
     
       6. The process of claim 1 wherein in step (a) said contacting is effected in a plurality of stages in series. 
     
     
       7. The process of claim 1 wherein the foam phase and the aqueous liquid phase are removed from the oxidation zone in separate streams.